Audio controller, more than one input source.

**stimps** · 08-26-2004, 07:54 AM

Just a post to let you guys know what ive been working on. Ive got some CD4066 14pin DIN chips, (quad bilateral switch) on a vero board and hooked it up to my inputs and outputs to the amp. So far ive only tried it on the test bench and it seems to work. More testing later to see if it doesnt affect the sound quality too much. If the decrease in sound quality is noticable, ill ditch it.
This all started when i finished my incar PC and couldnt use my car's factory HU and on steering wheel radio and volume controls. Very frustrating in city traffic!:P
Ive got the PC in the front, USB sound card in the back, next to a 5 channel amp (5.1) The usb sound card feeds the front and rear pair of speakers, and the sub to the amp. The wiring for the speakers from the amp have taken over from the car's existing speaker wiring. I have connected a speaker to RCA converter to the car's old speaker wiring, to pick up the signal from the car's HU, and that then goes to this circiut.
So this circiut interupts the 5.1 channels from teh sound card to the amp and switches over to the HU signal.
I've found so far, that even tho the 4066 is not intended for audio use, it works just fine. But of course more work is needed to really see if there is any sound quality loss.
I hope this drawing isnt too confusing for you guys, it took me a while to do it...without mistakes...i hope

anyway, all it basically does, it connect the 5.1 in to the 5.1 chans out when you connect the audigy sound card control wire on (to positive power +12), 5 switches come on and route the signals
OR, when you leave that wire off, and connect power control to the OTHER control wire, then another set of 5 switches turns on and connects the two inputs to the five outputs. I hope that makes sense.
The 10Kohm resistors on the signal control wires are just to stop the signal floating above ground when they are not ON. If these were not there then they would not turn off straight away, and cause two signals to be on at once.

I would suggest connecting both control wires to a "or" switch, (double position, single throw switch) to positive, to make sure only one is on and never both.

**lookinco** · 08-26-2004, 01:01 PM

I have just been thinking about the exact same problem. Two sound source with only one speaker, amp system.

My headunit uses stereo and my PC give out 5.1dolby digital. I could either just have stereo output from my PC to my headunit and then goes to the speaker, but I think it's such a waste to not use the 5.1 when it's avaliable.

I am really interested in a device that would allow me to switch between source.

Actaully I have a question, my headunit is a Pioneer with indash screen. It has Dolby Pro Logic. When I have it on, it will seperate my stereo audio source into front left, center, front right, rear left, rear left, and sub. How does it compare with real 5.1 dolby digital ?

If I am playing a DVD movie with 5.1 out from the computer but only uses stereo output , when it goes into my headunit with the Dolby Pro Logic on, will I be losing a lot of special effects ?

**stimps** · 08-28-2004, 04:24 AM

Yes. Keep all your signals seperate. Thats why my circiut above looks so complicated and large. Its just that since non of the "switches" have any common's, i had to double up the number of switches i needed, to switch 5chans on together, for 5.1, or another 5chans on together, to downmix the stereo, into those seperate 5 chans. Get me?
Anyway, next week ill make up a etched board and start biulding

**AlienEclipse** · 09-20-2004, 06:47 AM

Any update on this project.

**stimps** · 09-21-2004, 09:36 AM

coming, I have finished biulding the prototype (on vero board) Im just worried about noise interference. I have been having one of those months when I cant string a few spare hours together so I can actually rip into this and install it!
Ill try tomorrow

Ive added a small transistor so it switches input channels automatically. If the ignition is on, but the PC is not, it routes from factory HU.
If the ignition is on and the PC is on, it routes from the PC.

**stimps** · 09-22-2004, 04:29 AM

Everything works, but its got two problems, Noise, and lots of it. Seems to be coming from the power supply for the audigy NX card next to it (5 volt switch mode supply) as the +12v that supplies power to this circiut, also supplies the 5 volt power supply. I can make this noise go totally away, ...if I just turn off the audigy nx :P
But thats not all, there is also some clipping/crosstalk between inputs. When I have the HU source turned on, it sound perfect, but if I turn up the volume level on the PC, some clipping/bass or something, sorta signals from the PC are getting thru. Dunno why.
And another thing, when you switch from source 1 to source 2, there is a noticable pop and click. So I might as well use a bloody relay now. *sigh*

End of project. *chucks it out*

Knew this project seemed too easy to be true:P I spose the positive side of this is now its been tried and you guys can avoid wasting your time with this kind of method. If you can find other more siutable IC's however and get rid of the nosie, then your on a winner.

**stimps** · 09-27-2004, 06:41 AM

well Ive finally got this thing up and working, without the above circiut. I simply used 4 relays! LOL
I found that you have to switch the grounds of the signals, as well as the signals. If you have the grounds tied together, the other source will inject noise into the first audio source. So by switching the approriate ground off as well as the signal, I can switch from my HU radio, cd player, or my PC without any noise. There is a click and a thud, but its no where near as bad as I feared.

I thought the noise was directly due to the above circiut i made, but it wasnt, it was the lack of switching the right grounds.

So in hindsight, the above circiut does work, however you have to add another whole set of ics to switch the grounds too! No way im going that far. You dont actually get any added benifit anyway, maybe a tiny bit less noise, not sure.

Just gotta keep looking for a better option, such as the noiseless, clickless audio switcher chips available from some of the electronics suppliers, but in a more home user freindly package.

**vberry** · 10-10-2004, 04:51 PM

I just did a more low tech version of this with relays and a pair of wiring harnesses. i have a bose factory system and got both molex plugs for the HU wiring harness (to be able to just plug inline with factory harness, no splicing of factory wires). I wanted to keep the factory headunit/amp/speakers, so using 4 radio shack dpdt relays switched only the speaker wires, keeping all other wires connected. So the HU power button still controls the amp power, and a spst switch on the relay power line switches between the factory hu and carpc input. Not an elegant solution(relays and harness just hang behind the HU) but cheap and functional (no noticable degredation of sound quality with speaker lines going through relays)

So im using an audigy 2nx for sound, the outputs to the factory amp work but the volume is too low. thinking about line drivers, but not sure what the factory amp is expecting, any ideas?

**stimps** · 10-10-2004, 08:12 PM

yeah most things are not loud enough on my system either. I just turn everything up. Gain on the amp up to max..and have to remember to turn the sound up high on the PC just before i play a DVD